1. Field of the Invention
The present invention relates in general to a highly efficient cell-cultivating device.
2. Description of the Related Art
The cell-cultivating industry is increasingly important due to the advances of biotechnology, and the corresponding market is continuously expanding. The characteristics of cells include: slow growth, easy damage by shearing forces and easy contamination by microbes, high cultivation cost, easy cultivation failure, and anchorage-dependence (for most cells). Due to these characteristics, the current cell-cultivating systems are not very successful. A general example of a cell-cultivating system is roller bottles. Each roller bottle can provide an area of only 850-1700 cm.sup.2 for cultivating cells. Therefore, thousands of roller bottles are simultaneously taken care of in the factories, requiring a great deal of labor. Automation of the roller-bottle cell-cultivating system can save labor, but is expensive. Another example of a cell-cultivating systems is a stir tank. The tank has microcarriers inside for growing cells thereon. In this example, however, stirring culture medium and gassing cells considerably threaten growth of the cells. Furthermore, the operation conditions need to be changed when the dimensions of the stirring tank are enlarged (the enlargement is of three dimensions) . Changes of the operation conditions greatly delay the product harvest. In addition, the cells tend to get contaminated when the stirring tank is enlarged. Another example of a cell-cultivating systems is hollow fibers, by which the cell density can be up to 10.sup.8. In this example, however, the reactor for cultivating cells is a plug-flow type. When the cell density increases to a predetermined level, the cells at the rear end of the reactor cannot obtain nutrition. To avoid such a situation, the reactor generally is not made large, which is the major disadvantage of the hollow fiber reactor. The device of the present invention adopts air/liquid circulation, and therefore is different from all the above-mentioned cell-cultivating systems.
U.S. Pat. No. 5,766,949 is most related to the present invention. It provides a system in which the culture medium oscillates up and down with respect to a substrate means provided in a cell-cultivating apparatus. Also, two storage tanks are provided for the culture medium circulating therebetween. A disadvantage of this system is that the culture medium in the storage tanks is not used to cultivate cells, and thus the use of the culture medium is not efficient. Furthermore, the use of a large substrate means it is necessary to increase the volumes of the storage tanks. Furthermore, two or more peristaltic pumps are simultaneously used to circulate the culture medium, so that control thereof is complicated.
Tissue engineering has been greatly developed in recent times. Artificial tissues such as artificial skins, artificial livers, artificial corneas and artificial blood vessels are produced outside human bodies. Because the number of elderly citizens and citizens suffering from burns or ulcers caused by diabetes are increasing from year to year, the market for artificial skins will be very large in the future. Thus far, the profits of selling artificial skins are very good, allowing companies not to consider reduction of cost by means of mass production. However, any commercial product in the end must face cost competitions. In addition, many kinds of tissue products, such as artificial blood vessels and artificial corneas are produced by processing layers of mammalian cells. Therefore, an apparatus for mass-producing layers of mammalian cells will be required in the future.
In "Biotechnology and Bioengineering, 1993", Leon M. Wilkins et al. disclose that cultivating skin cells requires a special environment. Specifically, simultaneously growing epithelial cells and endothelial cells to form an artificial skin of three-dimensional structure can be successful only at an air/liquid interface. It is common to use culture vessels to cultivate artificial skins. In this way, however, a culture vessel can produce only one piece of artificial skin. A great deal of labor and spaces are required to mass-produce artificial skins.
WO 98/24880 discloses a cell culture system in which a peelable polymer film is attached to a base of a flask. When a desired number of cells have been attached to the polymer film, the base is removed from the flask and the polymer film is peeled away from the base for applying to the patient. The system is advantageous because removing the artificial skin from the cell culture flask is convenient. However, a culture flask can only produce one piece of artificial skin. Therefore, such a method is not suitable for mass-production.